1. Field of Invention
The present invention pertains to the field of document authentication. More particularly, this invention relates to document authentication using the physical characteristics of the underlying physical media of the document.
2. Art Background
A wide variety of documents including event tickets, paper currency, stock certificates, securities, checks, and other legal documents, etc., are commonly subject to various types of forgery. For example, such documents may be copied using color copiers. In another example, ink may be stripped off of the paper which underlies an authentic document and a new image printed on the paper, thereby enabling conversion of a low face value document to a high face value document.
In some prior methods of document authentication, a water-mark and/or other object is inserted into the paper on which a document is printed. Such methods attempt to avoid forgeries by making it difficult to reproduce the characteristics of the paper which underlies a document. Unfortunately, such methods usually cannot prevent the stripping of ink from the original paper and the printing of a new image.